How to Set Up Reverse DNS (rDNS) on Your Dedicated IP

By Sparkforge Support Team ·Last reviewed May 3, 2026

Reverse DNS (rDNS) maps your dedicated sending IP to your company's hostname so recipients see your brand instead of a third-party label. Required for full white-labeling and better deliverability.

When recipients open your email, the From or Sender field can show your company name instead of "Sent by Mailgun" or another third-party service. That swap happens through reverse DNS (rDNS) — and it requires a dedicated IP.

Beyond branding, rDNS improves deliverability and trust. Properly configured, it tells mailbox providers your IP is tied to a legitimate domain, which lowers spam-flagging risk and keeps tracking consistent.

What Reverse DNS Actually Does

A normal DNS lookup converts a domain name into an IP address. Reverse DNS does the opposite — it takes an IP and returns the hostname tied to it. Works for both IPv4 and IPv6.

For email, rDNS verifies that your sending server's IP belongs to a legitimate domain (yourcompany.com instead of mailgun.org). This is separate from CNAME masking — rDNS configures the PTR record on your dedicated IP itself.

Common rDNS Mistakes

Missing or invalid PTR record

The PTR (Pointer) record is the core of rDNS. If it's missing, mailbox providers can't verify your sending IP. Make sure the PTR record is set and returns a valid hostname for your IP.

Hostname doesn't resolve back to the IP

The hostname returned by the PTR record needs to resolve back to the same IP that started the lookup. Example: if your PTR for 8.8.8.8 returns mail.yourwebsite.com, then mail.yourwebsite.com must resolve to 8.8.8.8. Mismatches break rDNS.

Hostname doesn't resolve at all

If the hostname in the PTR record returns nothing, mailbox providers won't trust the sender. Ensure the hostname has a valid A record pointing to your IP before you set up rDNS.

Set Up rDNS

Setting rDNS with multiple hostnames requires a dedicated IP. Shared IPs only support one hostname per IP, so they can't host multiple rDNS configurations.

Create the A record at your DNS provider. Format: A, mail.customer.com, 123.45.67.89 — pointing your chosen hostname to your dedicated IP.
Open Agency Settings → Email Service.
In the SMTP service tab, click Dedicated Domain And IP in the Sparkforge section.
Find your dedicated IP, click the three-dot menu, and choose Reverse DNS (PTR).
Enter the same hostname you set in your A record. Sparkforge updates the PTR on its end to match.

Once both sides line up, mailbox providers will resolve your sending IP back to your company hostname, completing the white-labeling.

Frequently Asked Questions

Do I need a dedicated IP for rDNS?

Yes, for multi-hostname rDNS. Shared IPs can only resolve to one hostname per IP, so they can't support custom rDNS for individual senders.

What's the difference between CNAME masking and rDNS?

CNAME masking hides the third-party domain in your DNS settings. rDNS controls what hostname mailbox providers see when they reverse-lookup your sending IP. Both contribute to white-labeling but they're separate configurations.

What if my PTR hostname doesn't resolve back to the IP?

rDNS will fail. The A record (hostname → IP) and the PTR record (IP → hostname) need to point to each other. Fix the A record at your DNS provider before retrying.

How long does rDNS take to propagate?

DNS changes typically propagate within a few hours, though full global propagation can take 24-48 hours depending on your DNS provider's TTL settings.

Can I set rDNS for multiple sending domains on one IP?

Yes — that's the main reason you need a dedicated IP. You can configure multiple hostnames on one dedicated IP and rotate sending across them.